1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive composition having antistatic property, and pressure-sensitive adhesive sheets and a surface protecting film obtained by formulating into a form of a sheet or a tape using the composition.
Pressure-sensitive sheets comprising an antistatic pressure-sensitive adhesive composition of the present invention is suitably used in plastic products on which static electricity is easily generated. Among them, particularly, the sheets are useful as antistatic pressure-sensitive adhesive sheets used in utilities disliking static electricity such as an electronic instrument, as well as a surface protecting film used for the purpose of protecting an optical member surface such as a polarizing plate, a wavelength plate, an optical compensating film, a light diffusion sheet and a reflecting sheet.
2. Description of the Related Art
A surface protecting film is generally used for the purpose of preventing a scratch or a stain produced at processing or conveyance of a subject to be protected by applying to a subject to be protected via a pressure-sensitive adhesive layer coated on a protecting film side. For example, for the purpose of preventing a scratch or a stain, a surface protecting film is applied to an optical member such as a polarizing plate and a wavelength plate used in a panel of a liquid crystal display via a pressure-sensitive adhesive layer.
When a liquid crystal display is produced with these optical members, since a surface protecting film become unnecessary, it is peeled and removed from an optical member. Since the aforementioned optical member, pressure-sensitive adhesive, and surface protecting film are constructed of a plastic material, they have high electrical insulating property and generate static electricity upon friction or peeling. Therefore, also when a surface protecting film is peeled from an optical member, static electricity is generated. Therefore, also when a protecting film is peeled from an optical member such as a polarizing plate, static electricity is generated. When a voltage is applied to a liquid crystal in the state where static electricity remains, orientation of a liquid crystal molecule is lost, and a defect of a panel is generated. Then, in order to prevent such the disadvantage, a surface protecting film is subjected to various antistatic treatments.
Previously, as an attempt to suppress the aforementioned electrification of static electricity, for example, a method of preventing electrification by adding a low-molecular surfactant to a pressure-sensitive adhesive, and transferring a surfactant from a pressure-sensitive adhesive to an adherend has been disclosed (for example, see Patent Publication 1). However, the low-molecular surfactant is easily bled on a surface of a pressure-sensitive adhesive agent and, when applied to a protecting film, staining of an adherend is feared. Therefore, when a pressure-sensitive adhesive with a low-molecular surfactant added thereto is applied to a protecting film for an optical member, there is a problem that optical property of an optical member is deteriorated.
In addition, a method of adding an antistatic agent comprising polyether polyol and alkali metal salt to an acryl pressure-sensitive adhesive to suppress an antistatic agent from bleeding on a surface of a pressure-sensitive adhesive has been disclosed (for example, see Patent Publication 2). However, also in this method, bleeding of an antistatic agent is not avoided, and it has been found out that, when applied to a surface protecting film, staining of an adherend occurs with time or under a high temperature.
Furthermore, a method for providing antistatic to the base polymer itself of a pressure-sensitive adhesive composition is disclosed as a means for reducing the aforementioned staining (see, for example, Patent Publication 3). In this disclosure, a pressure-sensitive adhesive composition made of a (meth)acryl-based polymer that contains a reactive surfactant is cited. However, great effects of suppressing the peeling electrification voltage on the adherend side that has not been electrification-prevented, according to this method, are not recognized, and as a result, it has been found that it is difficult to reduce staining and at the same time suppress the peeling electrification voltage on the adherend side that has not been electrification-prevented.
[Patent Publication 1] JP-A No.9-165460
[Patent Publication 2] JP-A No.6-128539
[Patent Publication 3] JP-A No.9-208910